The same types of workpieces are always worked with the same machine setting over long periods of time on hobbing machines. These machines are utilized in large-scale production. The workpieces are automatically supplied by loading devices and are removed again after being worked so that the operation of the machines, if they are adjusted for the working of a certain workpiece, is limited to the changing of worn tools (and possibly a change of the adjustment in relation to the new tool). Depending on the working conditions, a tool exchange is usually necessary after four to eight hours of use, thus after the cutting of teeth of a predeterminable number of workpieces. It is necessary to stop the machine during the time that the tool exchange is occurring, wherein the periods of disuse become still longer, if the adjuster is not there on time or cannot be there on time. In addition, a necessary cutter exchange is among others also disadvantageous, when the machine is to work beyond the normal working time, however, an adjuster is not available.
Starting out with these inadequacies, the basic purpose of the invention is to develop a method for the automatic exchange of the tool in hobbing machines and an apparatus for performing the method.
Devices for the automatic tool exchange in tool machines are know, for example in milling machines from German OS No. 25 25 364 or in turning machines from German OS No. 26 02 930. A transfer of these known tool-exchange systems onto hobbing machines is, however, not possible, because the insertion and chucking functions occur on both ends in the case of the hob, thus different conditions exist.
As a solution to the task, a method is first proposed, in which at least two gripping devices are provided, of which one removes the tool which must be exchanged, thus the work hob, from the working position of the machine and the other gripping device supplies a new tool, thus a new or reground hob, wherein the loading of the one gripping device and the unloading of the other is done by hand at any desired point in time.
This method can be performed differently for the space situations which exist on the machine. For example, it is possible to always perform both the loading and also the unloading operation outside of the machine, the one operation one time on the one side of the machine and the other operation on the opposite side. Other method steps, however, permit the unloading always on the same side of the machine and the loading always occurs at the same place above the working position, thus more in the center of the machine.
In all cases, the actual changing of the tool occurs automatically and the loading of the one gripping device with a new cutter or the unloading of the exchanged cutter in the other gripping device can take place at any desired point in time. In consideration of existing safety regulations, one will perform this operation, however, during inoperative times on the machine, preferably during the exchange of workpieces between two working cycles. For the inventive method for effecting the automated tool exchange, an apparatus is proposed in which the at least two gripping devices are movable along a shaft which is parallel with respect to the milling spindle and are pivotal about the axis of the shaft in the region of the cutter, which must be exchanged. A loading and unloading station exist on the path of movement.
Hobs often have shoulders which are cylindrical at both ends. Therefore, a gripping device is particularly suited for the apparatus according to the invention, which consists of two gripping means which are movably spaced from one another and are arranged on a common carrier, which gripping means grip and hold the respective cutter on the shoulders. However, it is also possible to use hobs, which are secured on a mandrel (for example according to German Gbm No. 76 16 406.2), wherein the pair of gripping means can then insert the tool unit on the mandrel which projects at both ends from the central opening of the cutter.
The gripping devices can be moved on a shaft or the like, which is rotatable through a certain angle, however, not movable axially, by a hydraulic cylinder. A hydraulic rotary piston or the like is provided for the rotary movement. In order that the gripping devices can also partake in the rotary movement, a carrier is provided on the shaft or the like.
A common longitudinal movement of the gripping devices and the swivellability of only one thereof is achieved by connecting the gripping devices to a coupling sleeve which permits the relative rotary movement and the nonswinging gripping devices are held by fixed guide bars or the like. The gripping device which is to be swivelled engages the carrier already prior to reaching and swivelling or exchange position, thus as long as it is still held by the guide bars.
It is of a particular advantage for the automated changing of the tool, if the devices which are needed for holding, guiding and moving of the gripping devices are arranged on the tool carrier, because then the new tools are always positioned parallel with respect to the milling spindle also in the case of an inclined position of the tool carrier, as it is necessary for cutting of helical workpieces.
It is furthermore preferable for the automated changing of the tool if the machine to which the inventive method is applied has devices for digital or other data input. The cutters which are used one after the other do not have the same dimensions, in particular diameters. Since in the case of the automated tool exchange, a suitable manual changing of the machine adjustment is not possible, it is then possible to feed in and store the aforemeasured values in order to automatically achieve after the cutter exchange a correspondingly corrected workpiece feed.
The machine control becomes simpler, if the automated tool exchange always takes place automatically from the respective shift position of the cutter at the same point on the shift path.
Various constructions are possible for the gripping means: They can be closed and opened hydraulically or, however, can be held in closed position by spring force and can be opened hydraulically against the spring force. The latter solution enhances operating safety.
It is preferable to construct the gripping means so that the cutter projects with a carrier cam into a corresponding recess in the gripping means, which is arranged such that the cutter is fed correctly aligned to the chuck, namely that the carrier cam projects into a corresponding recess in the milling spindle.
Compared with the known and generally common procedures for exchanging the tool in hobbing machines by hand, the method for the automated tool exchange according to the invention achieves a whole series of advantages not readily apparent from the illustrated sequence:
1. Longer running times for the machine until a manual procedure is necessary; the point in time of the manual procedure can be selected freely within wide limits;
2. Different cutter diameters can be determined outside of the machine and can be considered on the machine side;
3. The exchange of the cutter unit in a magazine requires less time by an expert on the machine;
4. The danger of injury to the operating personnel is less, the exchange requires less effort;
5. The danger of a tool damage during the tool exchange is almost impossible.